Séfar (in Arabic: سيفار) is an ancient city in the heart of the Tassili n'Ajjer mountain range in Algeria, more than 2,400 km south of Algiers and very close to the Libyan border. Séfar is the largest troglodyte city in the world, with several thousand fossilized houses. Very few travelers go there given its geographical remoteness and especially because of the difficulties of access to the site. The site is full of several paintings, some of which date back more than 12,000 years, mostly depicting animals and scenes of hunting or daily life which testify that this hostile place has not always been an inhabited desert. Local superstition suggests that the site is inhabited by djins, no doubt in connection with the strange paintings found on the site.

In 1950, the explorer Roger Frison-Roche made a crossing of more than a thousand kilometers on the back of a camel with the photographer Georges Tairraz II, in the heart of the Sahara, from Hoggar then Djanet in Algeria to Ghat in Libya. From their journey they brought back a large number of color films and documents. Among thousands of photos, they selected 47 images which reflect the various aspects of these immense spaces which occupy a third of Africa in the book "The Great Desert". “The Great Desert, 1000 kilometers on camelback” is the eponymous 85-minute documentary of this epic, released in 1950.